class Solution {
public:
    int peakIndexInMountainArray(vector<int>& arr) 
    {
        int left=0;
        int right=arr.size()-1;
        while (left < right)
        {
            int mid=left+(right-left+1)/2;
            if (arr[mid]>arr[mid-1])
                left=mid;
            else
                right=mid-1;
        }
        return left;
    }
};
